Chris Kresser: It’s a great question. We don’t see a lot of that. We certainly have seen patients who have reacted to Xifaxan or rifaximin, but I would say eight to nine times out of 10 it’s well tolerated. In fact, in many cases, patients don’t feel anything. They say it’s weird. Unlike other antibiotics that they’ve taken, which they definitely felt and noticed when they were taking them, they don’t notice any reaction to Xifaxan or rifaximin, in part probably because the vast majority of it is not absorbed systemically.
On the other hand, I just actually had a patient who I talked to that became significantly worse after taking rifaximin, and in this case, it was constipation. The patient had a tendency towards constipation, and then after they took rifaximin, they became significantly more constipated. It’s interesting. I’m not sure what to make of that because the studies that we’ve talked about in the curriculum suggested that rifaximin doesn’t significantly alter the colonic bacteria and, if anything, may improve it, and so I’m not really sure why that would happen, but it does happen in some cases.
As for how to decipher between a Herx reaction and adverse reaction, it’s pretty unlikely that … I guess it depends what you mean by “adverse.” I would say an allergic kind of response to the drug is pretty unlikely, especially because it’s not systemically absorbed. If adverse reaction means that it’s causing changes in their gut that are actually not helping them versus it’s causing changes in the gut that are going to be beneficial over the long term but are causing symptoms in the short term, I’d say that’s almost impossible to differentiate while they’re on the treatment, and the only way you’re going to know is by them stopping the treatment and seeing if they start to improve at that point.